Challenges occur in the guiding of light from one type of waveguide to another, for example, from a ridge waveguide to a so-called “strip-loaded” ridge waveguide. A ridge waveguide involves an isolated waveguide rectangle, while a strip-loaded ridge waveguide comprises a multi-layer section with at least one fairly thin waveguide contact region connected to one or both sides of a central waveguide rectangle.
A key challenge in waveguide photonics is building waveguides with different depths of strip-loading or ridge waveguides without strip-loading at all, all in the same process. Strip-loading refers to a small connection of waveguide that is left at the edge of a ridge waveguide, typically for electrical contact. The typical approach is to utilize multiple etch steps in series. Different parts of the waveguide are exposed at different times. In locations where deeper or even complete etching surrounding the waveguides is available, the waveguide will usually have been exposed to multiple etches. This leads to “interface effects” on the edge of the waveguide where multiple etch steps have been executed, which can lead to performance problems.
An object of the present invention is to overcome the shortcomings of the prior art by providing a multi-layer optical device and a method of manufacturing a multi-layer optical device, which minimizes locations undergoing multiple etches.